CN113751049B - Preparation method, product and application of titanium carbide/carbon nitride composite photocatalyst - Google Patents
Preparation method, product and application of titanium carbide/carbon nitride composite photocatalyst Download PDFInfo
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- CN113751049B CN113751049B CN202111202849.3A CN202111202849A CN113751049B CN 113751049 B CN113751049 B CN 113751049B CN 202111202849 A CN202111202849 A CN 202111202849A CN 113751049 B CN113751049 B CN 113751049B
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
- B01J27/24—Nitrogen compounds
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
- B01J27/20—Carbon compounds
- B01J27/22—Carbides
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- B01J35/23—
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- B01J35/39—
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- B01J35/612—
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- B01J35/633—
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
- C01B3/02—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen
- C01B3/04—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by decomposition of inorganic compounds, e.g. ammonia
- C01B3/042—Decomposition of water
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/36—Hydrogen production from non-carbon containing sources, e.g. by water electrolysis
Abstract
The invention provides a preparation method of a titanium carbide/carbon nitride composite photocatalyst, which comprises the following steps: (1) Mixing titanium aluminum carbide and hydrofluoric acid, stirring, centrifuging, cleaning, and dispersing in water to obtain titanium carbide suspension; (2) Calcining the carbon nitride precursor and then carrying out protonation treatment to obtain protonated carbon nitride; (3) And mixing the titanium carbide suspension with protonated carbon nitride, stirring and carrying out self-assembly to obtain the titanium carbide/carbon nitride composite photocatalyst. The preparation method of the titanium carbide/carbon nitride composite photocatalyst is simple to operate and easy to realize industrialization. The titanium carbide/carbon nitride composite photocatalyst prepared by the preparation method has the advantages of wide light energy utilization range and high catalytic activity, can effectively improve the hydrogen production rate and has stable performance, simple operation, low cost and higher practical value when being applied to the photocatalytic hydrogen production process.
Description
Technical Field
The invention belongs to the technical field of catalyst preparation, and particularly relates to a preparation method, a product and application of a titanium carbide/carbon nitride composite photocatalyst.
Background
With the continuous advance of urbanization, carbon dioxide (CO) generated by combustion of fossil fuel 2 ) Emissions have increased dramatically, leading to an increasing global ecological and energy crisis. Hydrogen (H) 2 ) The method has the advantages of cleanness, sustainability, storage and high energy density, so the high-efficiency acquisition, storage and utilization of the method are considered as important ways for replacing fossil fuels and realizing carbon neutralization, wherein the photocatalytic hydrogen production by using hydrogen-rich chemicals is one of the most potential hydrogen production technologies with energy conservation and environmental protection. However, conventional photocatalysts are directed to the sunThe energy utilization rate is not high, the hydrogen yield is relatively low, and the practical application requirements are difficult to meet; moreover, the catalyst is mostly doped with noble metal materials such as Pt, so that the cost is high. In recent years, graphite phase carbon nitride (g-C) 3 N 4 ) Although the noble metal catalyst has been actively used as a substitute for the conventional noble metal catalyst in many reactions, how to further improve the photocatalytic hydrogen production efficiency is still a topic of much attention of researchers.
C 3 N 5 Is another carbon nitride framework material originally prepared by Gillan in 2000. Compared with g-C 3 N 4 ，C 3 N 5 Having a narrow band gap (C) 3 N 5 About 2.0eV of C 3 N 4 About 2.6 eV), high negative conduction band potential (C) 3 N 5 about-1.46eV 3 N 4 About-1.1 eV), and the structure contains more N, including secondary nitrogen atoms in amino groups at edge positions, triazole-based conjugated units and N-N coupling structures which are favorable for reactant molecule adsorption and electronic interaction. Wherein, the lone pair electron in the coupled N atom may be an active catalytic center for exciting electron shuttle in the sigma-pi channel, and it can also be used as an adsorption center for adsorbing H by electron interaction from conjugated ring 2 O and other reactants. Thus, C 3 N 5 Is a substitute for g-C 3 N 4 The ideal photocatalyst of the compound. However, C alone 3 N 5 When the catalyst is applied to the process of preparing hydrogen by photocatalytic water, the catalytic effect is poor, and the hydrogen production rate is low.
Disclosure of Invention
C is to be 3 N 5 In combination with a suitable promoter, the reactivity can be further improved, and the metal promoter captures photogenerated carriers (e) from the semiconductor due to its unique Fermi level - Or h + ) Weakening the recombination rate of carriers and acting as a redox reaction center.
In order to solve the problems of the prior art, the present invention provides a titanium carbide/carbon nitride (C) alloy based on the above analysis 3 N 5 ) The preparation method of the composite photocatalyst is simple to operate and easy to realize industrialization.
The invention also provides the titanium carbide/carbon nitride composite photocatalyst prepared by the preparation method, and the catalyst has high hydrogen production rate and low use cost in illumination.
The invention also provides an application of the titanium carbide/carbon nitride composite photocatalyst in photocatalytic water hydrogen production.
A preparation method of a titanium carbide/carbon nitride composite photocatalyst comprises the following steps:
(1) Mixing titanium aluminum carbide and hydrofluoric acid, stirring, centrifuging, cleaning, and dispersing in water to obtain titanium carbide suspension;
(2) Calcining the carbon nitride precursor and then carrying out protonation treatment to obtain protonated carbon nitride;
(3) And mixing the titanium carbide suspension with protonated carbon nitride, stirring and carrying out self-assembly to obtain the titanium carbide/carbon nitride composite photocatalyst.
In the titanium carbide suspension obtained in the step (1), the titanium carbide can adopt an expression Ti 3 C 2 T x Is represented by, wherein, T x Representing the terminal groups O, OH and/or F, mainly present at the edges of the titanium carbide. The expression of carbon nitride is C 3 N 5 。
Titanium carbide (Ti) 3 C 2 T x ) Is a typical two-dimensional (2D) layered material that features high surface area, excellent electrical and optical properties, hydrophilicity, metallic properties, high elastic modulus, and carrier mobility. However, the titanium carbide nano material has poor stability and is easily oxidized into TiO in the air 2 And is inactivated.
In the preparation method, negative charges on the surface of the titanium carbide are utilized, so that the titanium carbide and the protonated carbon nitride are subjected to self-assembly through electrostatic interaction to form a titanium carbide/carbon nitride heterojunction (titanium carbide/carbon nitride composite photocatalyst). Due to the difference of electronic structure, electrons in the carbon nitride flow to the titanium carbide, so that more electrons in the terminal group O atom on the surface of the titanium carbide are promoted to carry out H 2 Reducing O to produce hydrogen to make the O atom capable of adsorbing H 2 O and reducing the O to generate the active site of hydrogen. At the same time, ti 3 C 2 T x /C 3 N 5 Formation of heterojunction, compared to pure carbon nitride (C) 3 N 5 ) The band structure of the titanium carbide/carbon nitride composite photocatalyst is adjusted, the conduction band is negatively shifted, the band gap is narrowed, and the titanium carbide/carbon nitride composite photocatalyst has photoresponse to all ultraviolet-visible light-near infrared bands.
The preparation method of the invention prepares Ti by electrostatic self-assembly 3 C 2 T x /C 3 N 5 Composite structures, on the one hand, can regulate C 3 N 5 Of Ti 3 C 2 T x The graphite phase carbon generated in the in-situ oxidation process can promote the photocatalytic hydrogen production activity by improving the affinity to water.
In the above technical scheme, in the step (1):
preferably, the concentration of the hydrofluoric acid is 10 to 50wt%. More preferably 35 to 45wt%. Still more preferably 40wt%.
Preferably, the stirring time is 2 to 48 hours. More preferably 12 to 28 hours. Still more preferably 24 hours.
Titanium aluminum carbide (Ti) 3 AlC 2 ) The titanium carbide obtained after exfoliation in hydrofluoric acid (HF) is a bulk material stacked in layers, and in order to obtain a better catalytic activity, it is preferable to obtain a titanium carbide suspension subjected to exfoliation in layers (nano rod-like sheets) by ultrasonic exfoliation after dispersing the titanium carbide in water for 1 to 5 hours. More preferably, the sonication time is 2 to 4 hours. Still more preferably 3 hours.
Preferably, the concentration of titanium aluminum carbide in hydrofluoric acid is 20 to 30g/L. Further preferably 25g/L.
Preferably, the water used to prepare the titanium carbide suspension is ultrapure water.
In the above technical solution, in the step (2):
preferably, the carbon nitride precursor is placed in a muffle furnace for calcination, and carbon nitride powder is obtained.
Preferably, the carbon nitride precursor is selected from one or more of 3-amino-1, 2, 4-triazole, 5-amino-1H-tetrazole, cyanuric acid and barbituric acid. More preferably 3-amino-1, 2, 4-triazole.
Preferably, the calcination temperature of the carbon nitride precursor is 400-600 ℃, and the heating rate is 3-10 ℃/min.
When the calcination temperature is too low, the polymerization degree of carbon nitride is low, and an effective pi electron system is difficult to form; when the calcination temperature is too high, the precursor is excessively decomposed, and an effective carbon nitride structure is also difficult to form, and preferably, the calcination temperature of the carbon nitride precursor is 500 ℃, and the temperature rise rate is 5 ℃/min.
Preferably, the calcination time is 2 to 4 hours. Further preferably 3 hours.
In order to prevent the powder from being scattered by the gas flow during the calcination, the carbon nitride precursor is preferably calcined in a crucible with a lid.
Preferably, the carbon nitride is protonated with hydrochloric acid. Since the carbon nitride structure contains a free amino group, a protonation reaction can be performed under acidic conditions, and the surface of the carbon nitride structure is positively charged. After the protonated carbon nitride is mixed with the titanium carbide suspension, the protonated carbon nitride can be self-assembled with titanium carbide with negative charges on the surface through electrostatic interaction to form a stable composite structure.
More preferably, 100mg of C is used 3 N 5 The molar weight of the hydrogen chloride in the added hydrochloric acid is 10-100 mmol. More preferably 50 to 70mmol. More preferably 60mmol.
Preferably, the protonation treatment is carried out for 2 to 6 hours. More preferably 3 to 5 hours. Still more preferably 4 hours.
In the above technical solution, in step (3):
preferably, C is protonated at 100mg 3 N 5 The addition amount of the titanium carbide is 50-200 mg calculated by titanium aluminum carbide. More preferably 100 to 150mg. Still more preferably 125mg.
Preferably, the protonated carbon nitride is mixed in suspension with the titanium carbide suspension. The specific operation is as follows: dispersing protonated carbon nitride in water to prepare protonated carbon nitride suspension; the protonated carbon nitride suspension and the titanium carbide suspension are then mixed.
Of course, the protonated carbon nitride may be directly dispersed in the titanium carbide suspension and mixed.
As a further preference, the water used for preparing the protonated carbon nitride suspension is ultrapure water.
More preferably, the titanium carbide suspension is added dropwise to the protonated carbon nitride suspension so that both are in sufficient contact with each other.
Preferably, the time for stirring self-assembly is 1 to 4 hours. Further preferably 3 hours.
Preferably, after the self-assembly is finished, the reaction solution is centrifuged and vacuum-dried to obtain the titanium carbide/carbon nitride composite photocatalyst.
When the titanium carbide/carbon nitride composite photocatalyst prepared by the preparation method is used for hydrogen production, the hydrogen production rate can be improved after the titanium carbide/carbon nitride composite photocatalyst is recycled. The principle is that in illumination, ti-C bonds at the edges of titanium carbide can be broken to generate nano-sized graphite phase carbon and TiO in situ 2 And forming graphene (C-C) quantum dots and titanium dioxide (TiO) 2 ) And (4) quantum dots. The absorption of light by the catalyst is enhanced by the pi-pi + electronic transition of the graphitic carbon. Meanwhile, the results of Density Functional Theory (DFT) calculation prove that H 2 O in graphene (002)/C 3 N 5 The adsorption energy on the interface is (-1.997 eV) which is higher than that of the original Ti 3 C 2 O 2 (001)/C 3 N 5 The interface (-0.518 eV) is more negative, which shows that the graphene (002)/C is generated in situ 3 N 5 H is more easily adsorbed at the interface 2 O, thereby promoting H 2 And (3) producing hydrogen by catalytic reduction of O.
A titanium carbide/carbon nitride composite photocatalyst is prepared by the preparation method of any one of the titanium carbide/carbon nitride composite photocatalysts. The titanium carbide/carbon nitride composite photocatalyst has a wide light energy utilization range, is applied to photocatalytic hydrogen production, and is simple to operate, high in hydrogen production rate and stable in performance.
An application of the titanium carbide/carbon nitride composite photocatalyst in photocatalytic water hydrogen production. The specific operation is as follows:
when the titanium carbide/carbon nitride composite photocatalyst is used for photocatalytic hydrogen production, the titanium carbide/carbon nitride composite photocatalyst is directly put into a sacrificial agent aqueous solution, and the hydrogen can be produced by illumination. And the hydrogen production rate is high, the light energy utilization range is wide, the operation is very simple, and the practical value is very high.
Preferably, the sacrificial agent is one or more of triethanolamine, methanol, sodium sulfide and sodium sulfite. More preferably triethanolamine. In the aqueous solution of the sacrificial agent, the concentration of the triethanolamine is preferably 5 to 20wt%. Still more preferably 10% by weight.
Preferably, the amount of the titanium carbide/carbon nitride composite photocatalyst added is 0.25 to 1g/L. More preferably 0.5 to 0.9g/L. Still more preferably 0.75g/L.
Preferably, the wavelength of light is 300 to 1100nm.
The light source for illumination is preferably a xenon lamp with a power of 250 to 350W. More preferably, the light source power is 300W.
Preferably, the distance between the light source and the photocatalytic reactor is 2-10 cm. Further preferably 4cm.
In addition, in order to ensure that the titanium carbide/carbon nitride composite photocatalyst is uniformly dispersed in a photocatalytic reaction system, magnetic stirring is carried out in the reaction process, and the reaction temperature is maintained to be 25 ℃ through a circulating cooling system.
Compared with the prior art, the invention has the beneficial effects that:
the preparation method of the titanium carbide/carbon nitride composite photocatalyst is simple to operate and easy to realize industrialization. The titanium carbide/carbon nitride composite photocatalyst prepared by the preparation method has the advantages of wide light energy utilization range and high catalytic activity, can effectively improve the hydrogen production rate and has stable performance, simple operation, low cost and higher practical value when being applied to the photocatalytic hydrogen production process.
Drawings
In FIG. 1:
(a) High-fraction transmission electron microscope images of the titanium carbide nanorod-shaped sheets in example 2 under different magnifications respectively;
(d) To (f) are respectively pure C in comparative example 1 3 N 5 Scanning electron microscope and transmission electron microscope images;
(g) (ii) images of a scanning electron microscope and a transmission electron microscope of TC/CN-15 in example 2 respectively;
in fig. 2:
(a) Is pure C in comparative example 1 3 N 5 X-ray diffraction patterns (XRD) of the multilayer stacked titanium carbide of comparative example 2 and TC/CN-15 of example 2;
(b) Is pure C in comparative example 1 3 N 5 Fourier Infrared absorption Spectroscopy (FTIR) of the multilayer stacked titanium carbide of comparative example 2 and TC/CN-15 of example 2;
FIG. 3 shows pure C in comparative example 1 3 N 5 X-ray photoelectron spectroscopy of titanium carbide stacked in multiple layers in comparative example 2 and TC/CN-15 in example 2;
FIG. 4 shows pure C in comparative example 1 3 N 5 X-ray photoelectron spectroscopy of multilayer stacked titanium carbide in comparative example 2 and TC/CN-15 in example 2;
wherein: (a) And (b) are respectively pure C in comparative example 1 3 N 5 Mapping and analysis of C1s and N1s with TC/CN-15 in example 2;
(c) And (d) respectively the Ti2p and O1s spectra and the resolution thereof for the multilayer stacked titanium carbide of comparative example 2 and TC/CN-15 of example 2;
in fig. 5:
(a) Is TC/CN-10, TC/CN-15, TC/CN-20, pure C 3 N 5 And ultraviolet-visible-near infrared (UV-vis-NIR) absorption spectra of multilayer stacked titanium carbide;
(b) Is TC/CN-15 in example 2 and pure C in comparative example 1 3 N 5 Corresponding (alpha h v) 1/2 And h v diagram;
in fig. 6:
(a) As C calculated by DFT 3 N 5 /Ti 3 C 2 O 2 /H 2 A charge density difference plot of O;
(b) Is C 3 N 5 /Ti 3 C 2 O 2 /H 2 The difference of the average charge density of the plane corresponding to the c axis of O is equal to the value of the isosurface
(c) Is C 3 N 5 、Ti 3 C 2 O 2 、Ti 3 C 2 O 2 /C 3 N 5 A free energy diagram of the hydrogen evolution reaction at the interface;
in fig. 7:
(a) And (b) respectively shows a Raman spectrum and an ultraviolet-visible absorption spectrum of the titanium carbide sheet suspension liquid after illumination for different time;
(c) Is the X-ray photoelectron spectrum of TC/CN-15 in example 2 after different illumination time;
FIG. 8 is a high resolution TEM image of TC/CN-15 from example 2 after 12 hours of illumination, wherein:
(a) For in situ generated TiO 2 (101) A crystal face;
(b) Is a graphene (002) crystal face generated in situ;
FIG. 9 is a view showing the structure at Ti 3 C 2 O 2 (001)/C 3 N 5 And graphene (002)/C 3 N 5 Optimized on model H 2 The charge differential distribution of the O molecules adsorption.
Detailed Description
The invention will now be further illustrated with reference to the following examples:
the raw materials used in the examples:
Ti 3 AlC 2 (200 mesh, purity)>98%) of 3-amino-1, 2, 4-triazole (purity) available from Fusmann technologies (Beijing, china)>96%) from mclin biochem technology limited (shanghai, china), and hydrofluoric acid (40 wt.%) and hydrochloric acid (36-38 wt.%) from the national pharmaceutical group chemicals, ltd (shanghai, china). All other chemicals were of analytical grade. Water level ultrapure water (resistance is more than or equal to 18.2M omega cm) used for experiment -1 )。
Examples 1 to 3
Will 1.0g Ti 3 AlC 2 The powder was slowly added to 40mL of concentrated HF solution (40 wt%) and kept under continuous stirring for 24h, resulting in multilayer stacked titanium carbide (Ti) 3 C 2 T x ). Washing the obtained multilayer titanium carbide with ultrapure water for several times until the pH value of the black suspension reaches 6-7; and re-dispersing the multi-layer titanium carbide after pH adjustment in 60mL of ultrapure water, and continuously performing ultrasonic treatment for 3 hours to obtain dark green supernatant containing the titanium carbide nanorod flakes, and marking as a titanium carbide flake suspension.
2.0g of 3-amino-1, 2, 4-triazole is placed in a 50mL corundum crucible with a cover at 500 ℃ and 5 ℃ for min -1 After calcining for 3 hours at the rate of temperature increase of (1), the residual brown C was collected 3 N 5 And ground into a fine powder. 200mgC 3 N 5 Dispersing the powder in 50mL of hydrochloric acid with the concentration of 1.2mol/L for protonation reaction, stirring for 4 hours, centrifugally separating and washing for a plurality of times, and re-dispersing in 15mL of ultrapure water again to obtain protonized C 3 N 5 And (3) suspension.
Then, different volumes of titanium carbide flake suspensions (i.e., 10, 15 and 20 mL) were added dropwise slowly to the protonation C described above, as shown in Table 1 3 N 5 To the suspension, stirring was carried out for 2.5 hours. Finally, the Ti is separated by centrifugation 3 C 2 T x /C 3 N 5 The composite material was then dried in a vacuum oven until all water was removed, yielding titanium carbide/carbon nitride composite photocatalyst samples corresponding to examples 1-3, designated as TC/CN-X (X =10, 15 and 20), respectively.
TABLE 1 amounts of protonated carbon nitride suspension and titanium carbide flake suspension added in examples 1-3
Comparative example 1
2.0g of 3-amino-1, 2, 4-triazole is placed in a 50mL corundum crucible with a cover at 500 ℃ and 5 ℃ for min -1 After calcining for 3h at the rate of temperature increase, the remaining brown sample was collected and ground to a fine powder to give pureC 3 N 5 。
Comparative example 2
1.0g of Ti 3 AlC 2 The powder was slowly added to 40mL of concentrated HF solution (40 wt%) and kept under continuous stirring for 24h. The obtained multilayer Ti 3 C 2 Washing with ultrapure water for several times until the pH value of the black suspension reaches 6-7, and drying in a vacuum oven until all water is removed to obtain the multilayer stacked titanium carbide.
Characterization of the catalyst 1
Titanium carbide nanorod flakes and protonated C 3 N 5 (protonation C 3 N 5 ) The zeta potentials of the two phases are-16.2 mV and 11.0mV, respectively, so that a stable complex is formed by strong electrostatic adsorption after mixing. The morphology of the composite (example 2) was observed by high resolution transmission electron microscopy and scanning electron microscopy, as shown in fig. 1. After the intensive ultrasonic treatment, the titanium carbide stacked in multiple layers is exfoliated and formed into titanium carbide nanorod-shaped sheets (as shown in (a) to (c) of fig. 1). Pure C obtained in comparative example 1 3 N 5 Has a block structure (as shown in (d) to (f) of FIG. 1). In FIG. 1, (g) to (i) show the titanium carbide nanorod flakes and protonated C 3 N 5 Significant recombination occurs and the nano-rod-shaped titanium carbide flakes are strongly attracted to C 3 N 5 A surface.
In the process of preparing the composite photocatalyst C 3 N 5 Needs to be protonated, therefore, C 3 N 5 The interlayer spacing increased due to electrostatic repulsion, as shown in Table 2, after recombination via N 2 The specific surface area and the pore volume measured by an isothermal adsorption model are obviously increased, thereby exposing more active sites and promoting the diffusion/migration of molecules and H 2 And (4) desorbing.
TABLE 2 TC/CN-15 from example 2 vs. pure C from comparative example 1 3 N 5 Specific surface area and pore volume comparison of
Characterization of the catalyst 2
TC/CN-15 obtained in example 2, pure C obtained in comparative example 1 3 N 5 And the chemical structure of the multilayer stacked titanium carbide prepared in comparative example 2 was characterized by XRD, FTIR and XPS. Wherein, the XRD and FTIR characterization results are shown in figure 2, and pure C 3 N 5 Shown as C in FIG. 2 3 N 5 The multilayer stacked titanium carbide is shown as Ti in FIG. 2 3 C 2 . As shown in FIG. 2 (a), more complete C is retained in TC/CN-15 3 N 5 Characteristic diffraction Peak, 27.5 ℃ corresponding to C 3 N 5 (002) Crystal planes, resulting from the interlayer stacking of conjugated aromatic CN sheets. Peak at 13.0 ° and C 3 N 5 (100) The crystal planes are related. Since the layered structure of the titanium carbide in TC/CN-15 is destroyed and the content is low, no obvious diffraction peak corresponding to the titanium carbide is found. In the Fourier infrared spectrum of (b) in FIG. 2, TC/CN-15 and pure C 3 N 5 Similar characteristic peaks are also shown. Furthermore, in TC/CN-15, 3435cm -1 The signal peak at (A) belongs to hydroxyl (-OH) at the edge of titanium carbide, 1103cm -1 Peak at and 1635cm -1 The peak at (a) can be attributed to the vibration of the C-F and C = O bonds, respectively, demonstrating protonated C 3 N 5 And the titanium carbide nano rod-shaped slice is compounded.
Using X-ray photoelectron spectroscopy (XPS) spectrum to TC/CN-15, pure C 3 N 5 And the surface chemical structure of the multilayer stacked titanium carbide were intensively studied, and as a result, pure C was shown in fig. 3 and 4 3 N 5 Shown as C in FIGS. 3 and 4 3 N 5 (ii) a The multilayer stacked titanium carbide is shown as Ti in FIGS. 3 and 4 3 C 2 . As shown in FIGS. 3 and 4, four elements of C, N, ti and O are simultaneously present in TC/CN-15. Wherein the C1s spectrum (FIG. 4 (a)) can be deconvoluted at 281.2, 284.8 and 288.1eV to three peaks, corresponding to C-Ti bonds, sp, in TC/CN-15 2 Hybrid C, C 3 N 5 Triazine C in (1). The fitted peaks at 398.7, 400.0, 401.0 and 404.6eV in the N1s spectrum (FIG. 4 (b)) are C = N-C, N- (C) 3, C-N-H edge amino group and π -excited, respectively, in TC/CN-15The effect of charge; and C 3 N 5 In contrast, the peak position of TC/CN-15 in the N1s spectrum exhibits a positive shift, indicating that an electron is donated from the electron donor C 3 N 5 To the electron acceptor titanium carbide promoter (titanium carbide nanorod flakes). As can be seen from the Ti2p spectrum (FIG. 4 (c)), no distinct tetravalent titanium peak was observed in the multilayer stacked titanium carbide, whereas in the TC/CN-15 sample, ti was present x O y Peak coating TiO 2 Peak substitutions (458.2 and 463.9 eV), which are probably due to chemical oxidation reactions between the weak Ti-O bonds at the edge sites and the hydroxyl groups. Two peaks at 529.3 and 529.6eV in the O1s spectrum (fig. 4 (d)) are attributable to the Ti-O bond and adsorbed O, while peaks at 531.6 and 532.3eV are the adsorbed hydroxyl groups Ti-OH and C-OH, respectively. XPS analysis demonstrated protonated C 3 N 5 And strong electron interaction between the interface of the titanium carbide nanorod flakes.
Characterization of the catalyst 3
The optical properties of the catalyst utilize ultraviolet-visible-near infrared (UV-vis-NIR) solid state absorption spectroscopy. As shown in FIG. 5 (a), TC/CN-10, TC/CN-15 and TC/CN-20 obtained in examples 1 to 3 all showed a photoresponse ranging from ultraviolet, visible light to near-infrared light, while pure C obtained in comparative example 1 3 N 5 (shown as C in the figure) 3 N 5 ) Exhibits poor light absorption in the near infrared region. TC/CN-15 and pure C were further determined using the Kubelka-Munk equation 3 N 5 (shown as C in the figure) 3 N 5 ) Band gap E of g (FIG. 5 (b)). Pure C 3 N 5 The band gap of (A) is 2.05eV, and the band gap of TC/CN-15 is calculated to be 1.85eV, indicating protonated C 3 N 5 The band gap becomes narrow after the titanium carbide nanometer rod-shaped slice is compounded. The band structures of semiconductors, especially their band positions (i.e., the Conduction Band (CB) edge and the Valence Band (VB) edge), have a large impact on photocatalytic HER performance. Respectively calculating TC/CN-15 and pure C by combining and analyzing the mott-Schottky diagram and the XPS valence band spectrum 3 N 5 The Conduction Band (CB) positions of (A) are-1.19 and-0.60 (V vs. NHE), respectively. As seen from Table 3, this significant negative shift in CB potential and narrowing of the band gap of the composite titanium carbide promoter improves the reducing power of the catalystThereby promoting H to a great extent 2 The precipitation rate of (c).
TABLE 3 TC/CN-15 in example 2 and pure C in comparative example 1 3 N 5 Band gap and band position of
Table 4 lists the results obtained by analyzing TC/CN-15 obtained in example 2 and pure C obtained in comparative example 1 3 N 5 Time Resolved Photoluminescence (TRPL) decay curves. Compared with pure C 3 N 5 Average lifetime of TC/CN-15 (τ) average ) From 5.35ns to 3.46ns; the decay τ average revealed the appearance of nonradiative decaying transitions, indicating the titanium carbide promoter and protonated C 3 N 5 Efficient exciton dissociation occurs between the interfaces, providing strong evidence for space charge separation in the TC/CN-15 heterointerface.
TABLE 4 TC/CN-15 in example 2 and pure C in comparative example 1 3 N 5 Mean lifetime of the medium quantum and its percentage contribution
Testing of catalyst Performance
A30 mg sample of the prepared catalyst was added to a flask containing 40mL of triethanolamine solution (10 wt%), followed by sonication for 30min. Then, high-purity nitrogen (N) gas is used 2 ) Bubbling was performed to remove residual air in the reactor. In the photocatalytic hydrogen evolution test, a light source (wavelength ranging from 300 to 1100 nm) was provided by a 300W xenon lamp. The irradiation distance between the xenon lamp and the reactor (flask) was set to 4cm. The reactor ensures that the catalyst sample is uniformly distributed in the suspension liquid under the magnetic stirring, and adopts a circulating cooling water systemThe system maintained the reactor temperature at 298K (+ -0.2K). The gas volume was measured and monitored by a gas chromatograph (GC-9200) equipped with a Thermal Conductivity Detector (TCD). Wherein the catalyst samples are TC/CN-10, TC/CN-15, TC/CN-20 and pure C respectively 3 N 5 And a multilayer stack of titanium carbide.
The catalyst performance was evaluated from a theoretical point of view by density functional calculations (DFT). The calculations were performed using the Vienna Ab-initio Simulation Package (VASP) code, using the full electron plane wave basis set and projector enhanced wave (PAW) method with an energy cut off of 520eV by the generalized gradient of spin polarization (GGA) and Perdewe-Burke-Ernzetrhof (PBE) functions. Sampling the Brillouin zone integral by adopting a (3 multiplied by 1) Monkhorst-Pack k point grid, and adopting a conjugate gradient algorithm in optimization. The convergence threshold on each atom was set to 1 × 10 -4 Total energy sum of eV
Hellman-Fieldman power. In or on>
The vacuum space avoids interference between adjacent systems.
Performance test example 1
Adopts the illumination experiment to evaluate TC/CN-10, TC/CN-15, TC/CN-20 and pure C 3 N 5 And the hydrogen generation rate of the multilayer stacked titanium carbide, the results are shown in table 5. As can be seen from Table 5, the composition with the titanium carbide nanorod flakes greatly improved C 3 N 5 The photocatalytic hydrogen production activity of (2) is considered to be caused by the combination of the titanium carbide nanorod flakes and the protonated C 3 N 5 The specific surface area and the pore volume of the photocatalyst are increased after the photocatalyst is compounded, the energy band structure is adjusted, and the space charge is effectively separated. Of these, TC/CN-15 showed the highest H 2 The formation rate was 506.57. Mu. Mol. G -1 ·h -1 Is almost pure C 3 N 5 4 times the rate of generation. However, further increases in the number of nanorod flakes of titanium carbide may instead result in H 2 Of rate of formationAnd (4) descending.
TABLE 5 rates of catalytic gas evolution with different catalysts
Performance test example 2
According to the characterization result, ti in TC/CN-15 is partially oxidized, so that when DFT calculation is carried out, a titanium carbide single layer (marked as Ti) with an O end is selected 3 C 2 O 2 ) As a calculation model, a single layer of Ti 3 C 2 O 2 (001) Is stacked on C 3 N 5 (001) Top of the sheet to build Ti 3 C 2 O 2 /C 3 N 5 A heterostructure. As can be seen from (a) and (b) in FIG. 6, the results of the difference in charge density and the difference in plane average charge density show that Ti 3 C 2 O 2 The O atom at the middle terminal is an effective active site for photocatalytic hydrogen production, and directional charge transfer is generated between the O atom and water molecules adsorbed on the surface. Bader charge analysis showed that approximately 0.14 electrons were injected into one water molecule. Thus, in the TC/CN-15 composite catalyst, C 3 N 5 From N to Ti 3 C 2 O 2 Migrate and pool around the terminal O atoms, facilitating the reduction of water. Meanwhile, as can be seen from (c) of FIG. 6, ti 3 C 2 O 2 /C 3 N 5 Heterostructure in Ti 3 C 2 O 2 /C 3 N 5 、Ti 3 C 2 O 2 And C 3 N 5 The lowest free energy barrier is shown, which is-0.168 eV (H is adsorbed on Ti 3 C 2 O 2 On the terminal O atom) to prove that the TC/CN-15 composite catalyst has the highest capability of producing hydrogen by hydrolyzing water.
Performance test example 3
To evaluate in example 2The prepared composite catalyst has stable catalytic performance, and the gas production rate is shown in table 6 after a circulating photocatalytic hydrogen production experiment is carried out on TC/CN-15. After 4 hours of continuous illumination hydrogen production experiments, the composite photocatalyst is dispersed in 10wt% of triethanolamine solution again after centrifugation and separation, and a second photocatalytic hydrogen production experiment is carried out for 6 times of continuous circulation. As can be seen from Table 6, the hydrogen yield increased significantly during the use of cycles 2 to 4, and then decreased slowly. Due to C 3 N 5 The structure is relatively stable, so that the change of chemical composition of the titanium carbide promoter may be the reason of the increase of catalytic activity. For this reason, the raman spectrum of the titanium carbide flake suspension in example 2 was measured, and the result is shown in fig. 7 (a). Two typical peaks belonging to the D and G bands are observed in fig. 7 (a), where the D band indicates disorder, while the G band is related to graphitic carbon properties. The intensity of the G-band increased with increasing light exposure time, indicating the formation of graphitic carbon species. The uv-vis absorption spectrum of the suspension of titanium carbide flakes in fig. 7 (b) reflects the gradual enhancement of light capture after illumination by the suspension of titanium carbide flakes, with a strong peak at 235nm after more than 9 hours of continuous illumination, which may be a pi-pi transition due to the increase of graphitic carbon.
TABLE 6 hydrogen yield during TC/CN-15 recycle in example 2
By XPS analysis of TC/CN-15 after different light irradiation times, as shown in (C) of FIG. 7, the Ti-C and Ti-X peaks in TC/CN-15 disappeared and Ti-O (TiO) in 3 hours after light irradiation 2 ) The intensity of the peak increases significantly. The disappearance of Ti-C and Ti-X peaks, the newly appeared Ti-O signal and the enhanced D-band intensity are caused by oxidation reaction at the edge position of a Ti-C bond, titanium dioxide and graphite phase carbon are generated in situ, and graphene (C-C) quantum dots and titanium dioxide (TiO) are formed 2 ) And (4) quantum dots. The peak intensity of tetravalent titanium further decreases with the increase of the light irradiation time, which is probably due to the oxidation of dioxide caused by the surface charge modificationDetachment of titanium nanoparticles. The result of observation of the TC/CN-15 subjected to illumination for 12 hours by a high-resolution transmission electron microscope is shown in FIG. 8, and in (a) of FIG. 8, lattice fringes with a spacing of 0.249nm appear on the surface of the composite photocatalyst, which are TiO 2 (101) A crystal plane, and in fig. 8 (b), a lattice stripe having a pitch of 0.368nm was observed as a graphene (002) crystal plane.
Performance test example 4
To demonstrate the increased hydrogen production rate due to oxidation of the titanium carbide tips, H was calculated by DFT 2 O molecule in Ti 3 C 2 O 2 (001)/C 3 N 5 And graphene (002)/C 3 N 5 The adsorption energy on the surface, the results are shown in FIG. 9. As can be seen in FIG. 9, H 2 O in graphene (002)/C 3 N 5 The adsorption energy (Eads) above is-1.997 eV, the ratio is Ti 3 C 2 O 2 (001)/C 3 N 5 More negative on (-0.518 eV), indicating H 2 O molecules are easier to adsorb on graphene (002)/C 3 N 5 At the interface, thus promoting H 2 And (4) carrying out catalytic reduction on O. Bader analysis showed that Ti 3 C 2 O 2 And graphene to H, respectively 2 O injects 0.14 and 0.09 electrons. Therefore, the graphite phase carbon (graphene (C-C) quantum dots) generated in situ can significantly improve the hydrogen production rate by enhancing the adsorption of water.
Claims (9)
1. A preparation method of a titanium carbide/carbon nitride composite photocatalyst is characterized by comprising the following steps:
(1) Mixing titanium aluminum carbide and hydrofluoric acid, stirring, centrifuging, cleaning, and dispersing in water to obtain titanium carbide suspension;
(2) Calcining the carbon nitride precursor and then carrying out protonation treatment to obtain protonated carbon nitride;
(3) Mixing the titanium carbide suspension with protonated carbon nitride, stirring and carrying out self-assembly to obtain the titanium carbide/carbon nitride composite photocatalyst;
the carbon nitride precursor is selected from one or more of 3-amino-1, 2, 4-triazole, 5-amino-1H-tetrazole, cyanuric acid and barbituric acid;
the carbon nitride is C 3 N 5 ；
The calcination temperature of the carbon nitride precursor is 400-600 ℃.
2. The method for preparing the titanium carbide/carbon nitride composite photocatalyst according to claim 1, wherein the concentration of the hydrofluoric acid is 10 to 50wt%.
3. The method for preparing the titanium carbide/carbon nitride composite photocatalyst according to claim 1, wherein in the step (2), the temperature rise rate is 3 to 10 ℃/min.
4. The method for preparing the titanium carbide/carbon nitride composite photocatalyst as claimed in claim 1, wherein in the step (2), carbon nitride is protonated with hydrochloric acid;
the molar weight of the hydrogen chloride in the added hydrochloric acid is 10-100 mmol based on 100mg of carbon nitride.
5. The method for preparing a titanium carbide/carbon nitride composite photocatalyst according to claim 1, wherein in the step (3), the amount of titanium carbide added is 50 to 200mg in terms of titanium aluminum carbide, based on 100mg of protonated carbon nitride.
6. The method for preparing the titanium carbide/carbon nitride composite photocatalyst as claimed in claim 1, wherein in the step (3), the protonated carbon nitride is mixed with the titanium carbide suspension in the form of suspension.
7. A titanium carbide/carbon nitride composite photocatalyst, which is prepared by the preparation method of the titanium carbide/carbon nitride composite photocatalyst as claimed in any one of claims 1 to 6.
8. The use of the titanium carbide/carbon nitride composite photocatalyst of claim 7 in photocatalytic water hydrogen production.
9. The use according to claim 8, wherein the titanium carbide/carbon nitride composite photocatalyst is added in an amount of 0.25 to 1g/L; the illumination wavelength is 300-1100 nm.
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